The present invention relates to an underfilling material for semiconductor packages. In particular, the present invention relates to an underfilling material which is used when a semiconductor package holding semiconductor elements on a carrier substrate is mounted onto a circuit board, a mounted board produced by such mounting, and a repairing method of a mounted board.
The above-described type of the mounted board is used in applications requiring high reliance such as automobile equipment, computers, and the like, and also mobile phones which have been mass-produced with the wide spread thereof. In general, such a mounted board is produced by mounting a semiconductor package holding semiconductor elements on a carrier substrate to a circuit board, that is, by bonding the semiconductor package onto the circuit board with solder balls.
In the case of mobile phones, bond-failure of the solder ball may occur by the deformation of the substrate caused by falling shock, external pressure generated with the operation of buttons, etc. Thus, a reinforcing method is employed by filling an underfilling material in spaces around the solder-bonded parts and curing it to seal them. As the underfilling material used to improve the reliability of the connection by reinforcing, one-pack type or two-pack type thermosetting epoxy-based materials containing epoxy resins, curing agents and plasticizers are widely and mainly used (cf. JP-A-10-204259).
However, the epoxy-based materials should be thermally cured for 30 minutes at 80xc2x0 C. or 10 minutes at 150xc2x0 C. When the low temperature curing properties are enhanced by the adjustment of compositions, the epoxy-based materials should be stored at a low temperature of about 5xc2x0 C. or less. In addition, when the epoxy-based materials are used as the underfilling materials, and the connection failures are found, the cured products, which are bonded to the circuit board, should be removed one by one, by heat melting them and/or swelling them with solvents in the repairing works after detaching the semiconductor package from the circuit board. Therefore, the conventional epoxy-based materials do not have satisfactory repairing properties required at the work spot.
One object of the present invention is to provide an underfilling material for a semiconductor package, which can achieve both the low temperature curing properties and the storage stability, and solve the above problems in repairing, that is, an underfilling material which can be cured at a temperature of at least 60xc2x0 C., for example, at 70xc2x0 C. for 20 minutes or at 80xc2x0 C. for 10 minutes, and can be stored at room temperature.
Another object of the present invention is to provide a novel mounted board comprising a semiconductor package holding semiconductor elements on a carrier substrate which is mounted on a circuit board.
A further object of the present invention is to provide a method for easily repairing a mounted board.
According to the first aspect of the present invention, there is provided a mounted board comprising a circuit board and a semiconductor package holding semiconductor elements on a carrier substrate, wherein said semiconductor package is connected to said circuit board with solder balls, and spaces between solder connected parts are filled with an underfilling material which consists essentially of a one-pack type thermosetting urethane composition.
According to the second aspect of the present invention, there is provide a method for producing a mounted board of the present invention, comprising the steps of:
connecting said semiconductor board to said circuit board with said solder balls,
then filling the spaces between solder connected parts with said underfilling material, and
curing said underfilling material to seal said mounted board.
According to the third aspect of the present invention, there is provided a method for producing a mounted board of the present invention comprising the steps of:
applying the surface of said circuit board with said underfilling material,
connecting said semiconductor board to said circuit board with said solder balls,
and curing said underfilling material to seal said mounted board.
According to the fourth aspect of the present invention, there is provide an underfilling material for a semiconductor package holding semiconductor elements on a carrier substrate mounted on a circuit board, consisting essentially of a one-pack type thermosetting urethane composition.
According to the fifth aspect of the present invention, there is provided a method for repairing a mounted board of claim 1 comprising the steps of:
partly heating at least one of said semiconductor package and said circuit board to a temperature in the range between 180xc2x0 C. and 350xc2x0 C.,
melting said cured underfilling material and optionally said solder,
removing said semiconductor package from said circuit board and
mounting said semiconductor package or a new semiconductor package on said circuit board.